Living in the central Australian desert has its problems,__o____ obtaining water is not the least.

问题描述:

Living in the central Australian desert has its problems,__o____ obtaining water is not the least.
为什么填of which
He _______ my letter that I sent last month.
A.replied to B.replied C.answered to D.answered for
为什么选A

of which=whose是名词所有格,表示"某某的"第一句话的意思是在澳大利亚中部的沙漠居住会(遇到)一些问题,它的取水(的问题)还不是最基本的.因为obtaining water是个动名词词组,是名词性质的,所以前面会用所有格来修饰
第二题reply to 表示回信,是个固定搭配